The polychlorinated biphenyls are persistent organic pollutants that cause many adverse effects on living beings. The objective of this research was to determine effects of PCB-77 on proliferation of CHO-K1 cell line. CHO-K1 cell line cultivated in Dulbecco's MEM medium suplemented with 10% FBS was applied as the test system for cytotoxicity determination of PCB-77. Test groups were treated with different concentrations of PCB-77 (25, 50, 75 and 100 μM). Cytotoxic effect was assessed by MTT method during 24, 48 and 72 h. After 72 h, dose respondent inhibition of proliferation amounted for 34.7-79.3%. IC values were derived from equations of related exponential trend lines interpolated in graphically presented correlation between % of cell growth inhibition and applied PCB-77 concentrations. IC50 for PCB-77 after 72 h was 43.1 μM. The results indicate that PCB-77 inhibits the proliferation of CHO-K1 cells. Inhibition of proliferation was proportional to increase of concentration of PCB-77.